CN101774013A - Composite grain finer for Mg-Al alloy and preparation method thereof - Google Patents

Abstract

The invention discloses a composite grain finer for Mg-Al alloy and a preparation method thereof. The composite finer comprises the following components: 50-60 percent of Al, 1-5 percent of C, 5-10.5 percent of Ca or 5-10.5 percent of Sr, and the balance of Mg. The preparation method comprises the following steps of: melting pure Al under 700-800 DEG C, adding Mg-CA or Mg-Sr intermediate alloy according to the formula, and compensating the insufficient Mg with pure Mg to obtain Al-Mg-Ca or Al-Mg-Sr intermediate alloy melt, cooling the melt to 600-650 DEG C, uniformly dispersing graphite powder into the melt by using a semi-solid stirring method, and casting to obtain the composite grain finer. The finer has the advantages of simple preparation method, easy batch production, easy control of the addition amount, no discharge of pollutant and particularly remarkable fining effect for the Mg-Al alloy with low Al content.

Description

Composite grain refiner for Mg-Al alloy and preparation method thereof

technical field

The present invention relates to a grain composite refiner for Mg-Al alloy and a preparation method thereof, in particular to a high-efficiency composite refiner containing graphite and alkaline earth metal (Ca or Sr) for Mg-Al alloy and its preparation method Preparation.

Background technique

Magnesium alloy is the lightest metal structure material. It has the advantages of light specific gravity, high specific strength, good vibration damping, strong electromagnetic shielding, and easy recycling. It is considered to be the most potential development and application in the 21st century. "Material. However, compared with iron and steel materials, the mechanical properties of magnesium alloy materials are still low, and further improving its strength, plasticity and toughness is very important for the promotion and application of magnesium alloys. It is well known that grain refinement is an important way to improve the strength and toughness of metal materials, and for magnesium alloys, the influence of grain size on its strength and plasticity is more significant than that of alloys with other crystal structures, and grain refinement can also significantly improve the strength and toughness of metal materials. Microstructure compactness of magnesium alloys. Therefore, the refinement of magnesium alloys by grain refinement technology is very important for the production of high-performance magnesium alloy products.

Traditional grain refinement methods, such as solid-state treatment, semi-solid forming, and casting grain refinement techniques, can refine magnesium alloys to varying degrees. Relatively speaking, the casting grain refinement technology represented by the microalloying method and the carbonaceous inoculant method has the advantages of simple operation, easy process control, and low cost. Among them, Zr is the most effective element for grain refinement of Mg, but because Zr reacts easily with Al to form the compound Al ₃ Zr, Zr cannot effectively refine the Mg-Al series cast magnesium alloy which is most widely used in industrial production. Alkaline earth metals are the most effective refining elements in the microelement alloying method for the refinement of Mg-Al cast magnesium alloys. grain growth. However, as the content of alloying elements increases, the refinement of Mg grains will soon reach saturation, and new alloy phases will be formed, resulting in a decrease in elongation and plasticity. The carbonaceous inoculant method mainly uses the C atoms produced by the decomposition of C-containing substances in the magnesium melt to combine with Al to form Al ₄ C ₃ particles with a structure similar to that of α-Mg and a similar lattice constant as the nucleation core. .

According to the basic theory of solidification, the final grain size of cast products is mainly controlled by the following two factors: one is the nucleation ability of crystal nuclei and the number of effective crystal nuclei; the other is the segregation of solute elements and their inhibition of grain growth ability. The stronger the nucleation ability of crystal nucleation, the smaller the kinetic undercooling (T _n ) required for crystal growth; the higher the segregation ability of solute elements, the stronger the ability to inhibit grain growth.

Among the published patents on carbonaceous refinement of magnesium alloys, Chinese patent publication No. CN1410566 and patent application CN1583327A relate to the technology of using carbon powder (graphite powder) alone as a carbon source to refine magnesium alloys. Based on the aforementioned idea of compound refinement, Chinese patent publication No. CN101135013 discloses a compound refiner containing carbon and rare earth Ce and a preparation method thereof. The literature [Metall.Mater.Trans., 2005: p2669] gives that the inhibitory factors of Ca, Sr and Ce to the growth of Mg grains are 11.84, 3.51 and 2.74, respectively. Compared with Ca and Sr, Ce has an The grain growth inhibition is relatively low. In the above three published patents, the preparation process includes the steps of mixing, drying, pressing and sintering of aluminum powder, graphite powder and magnesium powder. The main problem is that the aluminum powder and magnesium powder are easy to oxidize during the preparation process. , it is difficult to accurately control the composition of the refiner. However, the Chinese patent with the publication number CN1410566 and the patent application with the publication number CN1583327 only utilize the thinning effect of carbon powder, and compared with the compound thinning, its thinning effect is relatively limited.

Contents of the invention

The object of the present invention is to overcome the defective of prior art, provide a kind of grain composite refining agent for Mg-Al alloy and preparation method thereof, the present invention utilizes carbon and alkaline earth metal (Ca or Sr) to prepare a compound Efficient grain refiner. The method of the present invention is aimed at the Mg-Al alloy, and the carbon-containing inoculant method and the _melt micro-alloying method are combined and applied, and the dual effect of the high nucleation ability of the _Al4C3 particles and the effective inhibition of the grain growth of the alloying elements is utilized. A new high-efficiency refinement method is obtained. The grain composite refiner of the present invention has better refinement effect, especially for the refinement effect of wrought magnesium alloys with low Al content represented by AZ31.

The purpose of the present invention is achieved through the following technical solutions.

The selected carbon source is required to be non-polluting and easy to disperse during the preparation process. Alloying elements are required to have a higher ability to inhibit the growth of Mg grains, and are not easy to react with carbon sources.

The selected carbon source is graphite powder with a particle size of 8-15 μm;

The selected alloy elements are alkaline earth metals Ca and Sr, which are added in the form of master alloys.

A compound grain refining agent for Mg-Al alloy, which contains the following components: Al, C, Mg and Ca or Sr; the weight percentage of each component is: 50-60% Al, 1-5% C, 5% ～10.5% Ca or 5～10.5% Sr, the balance is Mg.

The method for preparing the grain compound refiner for Mg-Al alloy according to the present invention specifically comprises the following steps:

(1) Melt pure Al at 700-800°C, add Mg-Ca or Mg-Sr master alloy according to the formula, add insufficient Mg in the form of pure Mg, and obtain Al-Mg-Ca or Al-Mg-Sr master alloy melt ;

(2) Cool the Al-Mg-Ca or Al-Mg-Sr master alloy melt to 600-650°C, while stirring, slowly add graphite powder according to the formula, and then stir for 2-4 minutes to obtain a semi-solid melt;

(3) Pouring the semi-solid melt to obtain the compound grain refiner of the present invention.

The particle size of the graphite powder is 8-15 μm.

The stirring speed in step (2) is 200-500 r/min.

The formula is the weight percentage of each component in the compound grain refiner of the present invention: 50-60% Al, 1-5% C, 5-10.5% Ca or 5-10.5% Sr, and the balance is Mg.

The graphite powder was added above the center of the stirring vortex.

The method that composite refiner of the present invention uses is:

(1) Melt the Mg-Al alloy, stir the melt, remove the slag and keep it warm. In order to ensure the refining effect, the melt holding temperature should be between 740 and 760°C.

(2) Add the above-mentioned refiner block to the Mg-Al alloy melt, and the added amount is between 1.0-1.2% of the mass of the melt. The basic principle of adding amount control is to ensure that there is no graphite residue on the basis of the refinement effect, and there is no obvious growth of intermetallic compounds containing Ca or Sr.

(3) Add the refiner to the melt and keep it warm for 8-10 minutes, then manually stir it to ensure that the graphite powder is evenly dispersed in the Mg-Al melt and promote C and Al to form Al ₄ C ₃ phase. After stirring, the melt still needs to be kept warm for 10-12 minutes to ensure that enough Al ₄ C ₃ particles are formed and serve as nucleation cores of Mg grains.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) The present invention has a good refining effect on Al-containing magnesium alloys, especially for Mg-Al alloys with low Al content (≤6%). For example, for the AZ31 alloy, which is most widely used in industrial production with low aluminum content, compared with the AZ31 alloy without refinement treatment, the refinement degree after compound refinement can reach 4 to 5 times, and its strength after refinement treatment and elongation can be increased by 20% and 40%, respectively.

(2) The preparation method of the refiner is simple, and the refiner for the Mg-Al alloy in which the graphite powder is uniformly dispersed can be prepared. The composition of the grain refiner is easy to control, and it is easy to realize industrialized mass production.

(3) From the preparation to the use of the grain refiner, no pollutants are discharged, which is an environmentally friendly technology.

(4) After refinement treatment, there is no obvious new phase formation, and there is no problem of plasticity reduction caused by new phase formation.

Description of drawings

Fig. 1 is the XRD analysis result of Al-Mg-Ca-C composite grain refiner;

Fig. 2 is the XRD analysis result of Al-Mg-Sr-C composite grain refiner;

Fig. 3 is the XRD spectrum of Al-Mg-C grain refiner;

Fig. 4 is the metallographic structure of Mg-3Al alloy without refiner treatment;

Fig. 5 is the metallographic structure of Mg-3Al alloy treated with Al-Mg-C grain refiner;

Fig. 6 is the metallographic structure of Mg-3Al alloy through 0.2% Ca refinement treatment;

Fig. 7 is the metallographic structure of Mg-3Al alloy through 0.2% Sr refinement treatment;

Fig. 8 is the metallographic structure of Mg-3Al alloy treated with Al-Mg-Ca-C grain refiner;

Fig. 9 is the metallographic structure of Mg-3Al alloy treated with Al-Mg-Sr-C grain refiner;

Figure 10 is the metallographic structure of AZ31 magnesium alloy without refiner treatment;

Figure 11 is the metallographic structure of AZ31 magnesium alloy treated with Al-Mg-C grain refiner;

Fig. 12 is the metallographic structure of AZ31 alloy refined by 0.2% Ca;

Figure 13 is the metallographic structure of AZ31 alloy treated with 0.2% Sr refinement;

Figure 14 is the metallographic structure of AZ31 magnesium alloy treated with Al-Mg-Ca-C grain refiner;

Figure 15 is the metallographic structure of AZ31 magnesium alloy treated with Al-Mg-Sr-C grain refiner;

Figure 16 is the XRD patterns of AZ31 magnesium alloy treated with different refiners;

Figure 17 is the tensile stress-strain curve of AZ31 magnesium alloy treated with different refiners;

Figure 18 shows the tensile strength and elongation of AZ31 magnesium alloy treated with different refiners;

Figure 19 is the metallographic structure of AZ61 magnesium alloy without refiner treatment;

Figure 20 is the metallographic structure of AZ61 magnesium alloy treated with Al-Mg-C grain refiner;

Figure 21 is the metallographic structure of AZ61 magnesium alloy treated with Al-Mg-Ca-C grain refiner;

Figure 22 is the metallographic structure of AZ61 magnesium alloy treated with Al-Mg-Sr-C grain refiner;

Figure 23 is the XRD patterns of AZ61 magnesium alloy treated with different refiners;

Figure 24 is the metallographic structure of AZ91 magnesium alloy without refiner treatment;

Figure 25 is the metallographic structure of AZ91 magnesium alloy treated with Al-Mg-C grain refiner;

Figure 26 is the metallographic structure of AZ91 magnesium alloy treated with Al-Mg-Ca-C grain refiner;

Figure 27 is the metallographic structure of AZ91 magnesium alloy treated with Al-Mg-Sr-C grain refiner;

Figure 28 is the XRD patterns of AZ91 magnesium alloy treated with different refiners.

Detailed ways

In order to better understand the technical characteristics of the present invention, the present invention will be further described below in conjunction with the examples. It should be noted that the examples are not intended to limit the protection scope of the present invention.

Example 1 Preparation of Al-Mg-Ca-C Grain Composite Refiner

In this example, pure Al, pure Mg, Mg-30% Ca master alloy and graphite powder were used as raw materials to prepare an Al-Mg-Ca-C grain refiner. The preparation method of the Mg-30% Ca master alloy is as follows: put pure magnesium and pure Ca into a low-carbon steel crucible with a mass ratio of 7:3, then put it into a vacuum furnace, vacuumize and heat to 750°C, and melt Finally, the crucible is taken out, stirred properly, and cast into a mold to obtain the Mg-30%Ca master alloy.

The preparation method of Al-Mg-Ca-C grain compound refiner is: melt 55g of pure Al at 750°C, add 27g of Mg according to the formula (Ca8.1%, Al 55%, 3% C, and the rest is Mg) -30% Ca master alloy and 15g pure Mg to obtain an Al-Mg-Ca master alloy melt; the Al-Mg-Ca master alloy melt is cooled to 630°C and stirred at a stirring speed of 400r/min, While stirring, use a long-mouthed funnel to slowly add graphite powder with a particle size of 8-15 μm to the center of the stirring vortex in an amount of 3 g, and stir for another 3 minutes to obtain a semi-solid melt. Cast the semi-solid melt to obtain the grain compound refiner Al-Mg-Ca-C of the present invention.

Example 2 Preparation of Al-Mg-Ca-C Grain Composite Refiner

In this example, pure Al, pure Mg, Mg-30% Ca master alloy and graphite powder were used as raw materials to prepare an Al-Mg-Ca-C grain refiner. Its preparation method is: melt 50g of pure Al at 700°C, stir evenly, add 17g of Mg-30% Ca and 32g of pure Mg according to the formula (Ca 5%, Al 50%, C 1%, and the rest is Mg) to obtain Al-Mg-Ca master alloy melt; cool the Al-Mg-Ca master alloy melt to 600°C, and stir it at a stirring speed of 200r/min, while stirring, use a long-mouthed funnel to the center of the stirring vortex Slowly add graphite powder with a particle size of 8-15 μm in an amount of 1 g, and stir for 3 minutes to obtain a semi-solid melt. Cast the semi-solid melt to obtain the grain compound refiner Al-Mg-Ca-C of the present invention.

Example 3 Preparation of Al-Mg-Ca-C Grain Composite Refiner

In this example, pure Al, Mg-30% Ca master alloy and graphite powder were used as raw materials to prepare an Al-Mg-Ca-C grain refiner. Its preparation method is: melt 60g of pure Al at 800°C, stir evenly, add 35g of Mg-30%Ca according to the formula (10.5% Ca, Al 60%, C 5%, the rest is Mg) to obtain Al-Mg-Ca Master alloy melt: Cool the Al-Mg-Ca master alloy melt to 650°C and stir it at a stirring speed of 500r/min. While stirring, slowly add a particle size of 8 to the center of the stirring vortex using a long-mouthed funnel. ~ 15 μm graphite powder, added in an amount of 5 g, and then stirred for 3 minutes to obtain a semi-solid melt. Cast the semi-solid melt to obtain the grain compound refiner Al-Mg-Ca-C of the present invention.

Example 4 Preparation of Al-Mg-Sr-C Grain Composite Refiner

In this example, pure Al, pure Mg, Mg-30% Sr master alloy and graphite powder were used as raw materials to prepare an Al-Mg-Sr-C grain compound refiner. The preparation method of the Mg-30% Sr master alloy is as follows: put pure magnesium and pure Sr into a low-carbon steel crucible with a mass ratio of 7:3, then put it into a vacuum furnace, vacuumize and heat to 750°C, and melt Finally, the crucible is taken out, stirred properly, and cast into a mold to obtain the Mg-30%Sr master alloy.

Its preparation method is: melting 55g of pure Al at 750°C, adding 27g of Mg-30%Sr master alloy and 15g of pure Mg according to the formula (Sr 8.1%, Al 55%, 3%C, and the rest is Mg) to obtain Al -Mg-Sr master alloy melt; cool the Al-Mg-Sr master alloy melt to 630°C, and stir it at a stirring speed of 400r/min, while stirring, use a long-mouthed funnel to slowly move to the center of the stirring vortex Graphite powder with a particle size of 8-15 μm was added in an amount of 3 g, and stirred for another 3 minutes to obtain a semi-solid melt. Cast the semi-solid melt to obtain the grain composite refiner Al-Mg-Sr-C of the present invention.

Example 5 Preparation of Al-Mg-Sr-C Grain Composite Refiner

In this example, pure Al, pure Mg, Mg-30% Sr master alloy and graphite powder were used as raw materials to prepare an Al-Mg-Sr-C grain compound refiner. Its preparation method is: melt 50g of pure Al at 700°C, stir evenly, add 17g of Mg-30%Sr and 32g of pure Mg according to the formula (Sr5%, Al 50%, C 1%, and the rest is Mg) to obtain Al -Mg-Sr master alloy melt; cool the Al-Mg-Sr master alloy melt to 600°C, and stir it at a stirring speed of 200r/min, while stirring, use a long-mouthed funnel to slowly move to the center of the stirring vortex Graphite powder with a particle size of 8-15 μm is added in an amount of 1 g, and then stirred for 3 minutes to obtain a semi-solid melt. Cast the semi-solid melt to obtain the grain composite refiner Al-Mg-Sr-C of the present invention.

Example 6 Preparation of Al-Mg-Sr-C Grain Composite Refiner

In this example, pure Al, Mg-30% Sr master alloy and graphite powder were used as raw materials to prepare an Al-Mg-Sr-C grain compound refiner. Its preparation method is: melt 60g of pure Al at 800°C, stir evenly, add 35g of Mg-30%Sr according to the formula (10.5%Sr, Al 60%, C 5%, and the rest is Mg) to obtain Al-Mg-Sr Master alloy melt: Cool the Al-Mg-Sr master alloy melt to 650°C and stir it at a stirring speed of 500r/min. While stirring, slowly add a particle size of 8 to the center of the stirring vortex using a long-mouthed funnel ~ 15 μm graphite powder, added in an amount of 5 g, and then stirred for 3 minutes to obtain a semi-solid melt. Cast the semi-solid melt to obtain the grain composite refiner Al-Mg-Sr-C of the present invention.

Example 7 Preparation of Al-Mg-C Grain Composite Refiner

In order to compare and illustrate the refining effect of the composite refining agent, this example uses pure Al, pure Mg and graphite powder as raw materials to prepare an Al-Mg-C grain refining agent containing only C. The preparation method is as follows: melt 55g of pure Al at 750°C, add 42g of pure Mg according to the formula (Al 55%, 3% C, and the rest is Mg) to obtain an Al-Mg master alloy melt; melt the Al-Mg master alloy Cool the body to 630°C and stir it at a stirring speed of 400r/min. While stirring, use a long-mouthed funnel to slowly add graphite powder with a particle size of 8-15μm to the center of the stirring vortex. The amount of addition is 3g, and then stir for 3 Minutes, a semi-solid melt is obtained. Cast this semi-solid melt to obtain Al-Mg-C grain refiner Al-Mg-C containing only C.

In order to test the refinement effect and application range of the prepared Al-Mg-Ca-C and Al-Mg-Sr-C composite refiner in the present invention, the following examples 8, 9, 10 and 11 are respectively for Mg -3Al, AZ31, AZ61 and AZ91 alloys were refined using Al-Mg-Ca-C, Al-Mg-Sr-C composite refiners and Al-Mg-C refiners containing only C, and their Refinement effect.

Example 8: Grain refinement treatment of Mg-3Al alloy

The present invention selects graphite powder as the carbon source to ensure the generation of Al ₄ C ₃ crystal nuclei, and simultaneously selects alkaline earth metals as Mg grain growth inhibitory elements. Figure 1 and Figure 2 show the Al prepared in Example 1 and Example 4. - XRD analysis results of two composite grain refiners of Mg-Ca-C and Al-Mg-Sr-C. For the two kinds of master alloys, Al ₄ C ₃ phase is formed in them, and elemental C, ie graphite, also exists. As for the alloying elements Ca or Sr, they all react with Al to form intermetallic compounds such as Al ₄ Ca, AlSr, and Al ₄ Sr during the preparation process.

In order to compare and illustrate the remarkable effects of the two composite grain refiners of Al-Mg-Ca-C and Al-Mg-Sr-C of the present invention, Example 7 of the present invention prepared Al-Mg-C grains containing only carbon Refining agent, Figure 3 is the XRD pattern of Al-Mg-C refining agent. In this alloy, Al ₄ C ₃ phase also exists, and elemental C, ie graphite, also exists.

Firstly, the Mg-3Al alloy containing only 3% Al is selected to be treated with the above three grain refiners, and the Mg-3Al alloy is the basic component of the most commonly used wrought magnesium alloy AZ31 in industrial production.

First, 50 g of pure Mg was weighed and melted at 750° C., and then pure Al was added and melted to form a Mg-Al melt. It should be noted that since all the grain refiners used contain Al, the Al element content in the added refiner needs to be considered when performing the melting ratio. After stirring the Mg-Al melt to remove slag, adding a refining agent, the added amount is 1.0-1.2% of the mass of the Mg-Al melt. The refining agents added in this example are prepared from Example 1, Example 4 and Example 7 respectively. The basic principle of adding amount control is to ensure that there is no graphite residue on the basis of the refinement effect, and there is no obvious growth of intermetallic compounds containing Ca or Sr. Add the refiner to the melt and keep it warm for 10 minutes, then manually stir it to ensure that the graphite powder is evenly dispersed in the Mg-Al melt and promote C and Al to form Al ₄ C ₃ phase. After stirring, the melt still needs to be kept warm for 10 minutes to ensure that enough Al ₄ C ₃ particles are formed and serve as nucleation cores of Mg grains.

For the Al-Mg-C refiner, when added to the Mg-Al melt, the elemental C will react with the Al in the Mg-Al melt as follows:

4Al+3C＝Al ₄ C ₃ (1)

The Al ₄ C ₃ phase has a high melting point (>2000°C) and has high stability in the Mg-Al melt, so the Al ₄ C ₃ phase existing in the Al-Mg-C will be accompanied by the new phase in the melt The generated Al ₄ C ₃ phase diffuses into the Mg-Al melt and acts as the nucleation core of Mg grains. The existence of a large number of Al ₄ C ₃ particles will promote the refinement of Mg grains.

For Al-Mg-Ca-C and Al-Mg-Sr-C composite refiners, the reaction shown in formula 1 will also exist and generate Al ₄ C ₃ phase, and Al ₄ C is inherently present in the refiner ₃ phases, _they will eventually be uniformly dispersed in the Mg _- Al melt and promote the refinement of Mg grains; Comparing the phase diagrams of Al-Ca and Mg-Ca, Al-Sr and Mg-Sr, it can be seen that in the temperature range of 740-760 °C, these intermetallic compounds will undergo the following decomposition reactions:

Al ₄ Ca＝4Al+Ca (2)

AlSr＝Al+Sr (3)

Al ₄ Sr＝4Al+Sr (4)

And exist in the form of elemental Ca or Sr in the melt. The concentration of Ca and Sr in the melt after decomposition depends on the holding temperature and holding time and the amount added. The basic principle of controlling the addition of Ca or Sr is to ensure that no obvious intermetallic compounds containing Ca or Sr are formed under the premise of fully exerting the refining effect.

In order to further compare the refining effects of C-containing refining agents (including Al-Mg-C, Al-Mg-Sr-C and Al-Mg-Ca-C), Mg-30%Ca and Mg- The 30% Sr alloy is used to refine the Mg-3Al alloy, and the addition of Ca and Sr is equivalent to the addition of Ca and Sr in the composite refiner.

Figures 4, 5, 6, 7, 8 and 9 show unrefined Mg-3Al, and Mg-3Al alloys treated with Al-Mg-C refiner, Mg-30% Ca and Mg-30% Microstructure photographs of Sr master alloy, Al-Mg-Ca-C and Al-Mg-Sr-C compound refiner treated. Comparing the grain size, it can be seen that after being treated with a refiner containing only C, its refinement degree is 3 times (in the present invention, the ratio of the grain size of the non-refinement treatment alloy to the grain size after refinement is defined for the degree of refinement). However, for the Mg-3Al alloy with only Ca and Sr added, its refining effect is slightly worse than that of the Mg-3Al alloy refined with C. However, after being treated with a composite refiner containing C and alkaline earth metals (Ca and Sr), the degree of refinement is further improved, and the degree of refinement can reach 5 times. It can be seen that carbonaceous inoculation can effectively refine the Mg-3Al alloy, and a more excellent refining effect can be achieved under the combined action of carbon and alkaline earth metals.

Example 9: Grain refinement treatment of AZ31 magnesium alloy

AZ31 magnesium alloy is the most widely used deformed magnesium alloy, and its composition is 2.8-3.2% Al, 0.6-0.9% Zn, 0.2-0.3% Mn, and the rest is Mg. This alloy is compounded with a small amount of Zn and Mn on the basis of Mg-3Al alloy. The purpose of adding Zn is to improve its strength, and Mn is mainly to eliminate the adverse effect of Fe in magnesium alloy.

AZ31 magnesium alloy was refined by using Al-Mg-C, Al-Mg-Ca-C and Al-Mg-Sr-C three refiners respectively. The treatment process before the refining treatment is basically the same as that of Example 8, except that pure Zn and Mg-Mn master alloy need to be added for Zn and Mn alloying treatment before the refining treatment. The refinement process is the same as in Example 8. The basic reaction and refining mechanism in the melt after refining treatment are basically the same as in Example 8.

Figures 10, 11, 12, 13, 14 and 15 show the unrefined AZ31 alloy, and the AZ31 alloy treated with Al-Mg-C refiner, Mg-30%Ca and Mg-30%Sr master alloy respectively , and the metallographic structure photo of Al-Mg-Ca-C and Al-Mg-Sr-C composite refiner treatment. Comparing the grain size, it can be seen that compared with the unrefined AZ31 alloy, after the refinement treatment containing only C, the AZ31 alloy grains are obviously refined, and the degree of refinement is 3 times. However, for the AZ31 alloy with only Ca and Sr added, its refining effect is slightly worse than that of the AZ31 alloy refined with C. However, for the AZ31 alloy treated with Al-Mg-Ca-C and Al-Mg-Ca-C composite refiner, the grain size is further refined, and the degree of refinement is further increased to 4 times. It can be seen that for the AZ31 magnesium alloy, carbonaceous inoculation also significantly refines its grain size, and a more excellent refinement effect can be obtained after the composite refinement treatment of carbon and alkaline earth metals.

Figure 16 shows the XRD patterns of unrefined AZ31 and AZ31 alloy treated with Al-Mg-C refiner, Al-Mg-Ca-C and Al-Mg-Sr-C compound refiner respectively. For the AZ31 alloy, its phase composition is mainly Mg and Mg ₁₇ Al ₁₂ . After the refiner treatment, its phase composition has no obvious change, and it is still mainly composed of Mg and Mg ₁₇ Al ₁₂ . It can be seen that for the AZ31 magnesium alloy, its phase composition will not change significantly after being treated with the above three refiners.

In this example, the unrefined AZ31 alloy was measured by a tensile testing machine, and the AZ31 alloy was treated with Al-Mg-C refiner, Mg-30%Ca and Mg-30%Sr master alloy, and Al - Strength properties of AZ31 magnesium alloy treated with Mg-Ca-C and Al-Mg-Sr-C composite refiner, as shown in Figure 17 and Figure 18. a, b, c, d, e and f in Figure 17 and Figure 18 correspond to the unrefined AZ31 alloy, and the Al-Mg-C, Mg-30%Ca and Mg-30%Sr master alloys, And Al-Mg-Ca-C and Al-Mg-Sr-C refined AZ31 alloy. Wherein Fig. 17 is the tensile stress-strain curve, and Fig. 18 is the average tensile strength and elongation. The results show that compared with the untreated sample, the strength and elongation of the AZ31 magnesium alloy refined by carbon modification alone are improved, and the strength and elongation of the AZ31 magnesium alloy are further improved after the compound refinement treatment of carbon and alkaline earth metal , and the improvement rate is about 20% and 40% respectively.

Example 10: Grain refinement treatment of AZ61 magnesium alloy

AZ61 magnesium alloy is another common wrought magnesium alloy in the AZ series of magnesium alloys. Compared with AZ31, its Al content is higher. Its basic composition is 5.8-6.2% Al, 0.6-0.9% Zn, 0.2-0.3% Mn, and the rest is Mg.

The AZ61 magnesium alloy was refined by using three refiners, Al-Mg-C, Al-Mg-Ca-C and Al-Mg-Sr-C prepared in Example 7, Example 1 and Example 4, respectively. The process before and after the melt refinement treatment is the same as that of Example 8 and Example 9, and the basic reaction and refinement mechanism in the melt after the refinement treatment are basically the same as those of Example 8.

Figures 19, 20, 21 and 22 show the unrefined AZ61, and the AZ61 alloy treated with Al-Mg-C refiner containing only C, and Al-Mg-Ca-C and Al-Mg-Sr- C Metallographic structure photo after treatment with two compound refiners. Comparing the grain size, it can be seen that compared with the untreated AZ61, the grain size of the refined AZ61 magnesium alloy is obviously refined. However, the grain size of the AZ61 magnesium alloy treated with the three refining agents has no obvious difference, and the degree of refinement is about 3 times compared with the untreated AZ61 magnesium alloy. It can be seen that for AZ61 magnesium alloy, carbonaceous inoculation can also significantly refine its grain size, but the compound refinement of alkaline earth metal and carbon cannot further improve its refinement effect.

Figure 23 shows the unrefined AZ61, and the AZ61 alloy was refined by the Al-Mg-C refiner containing only C, and the two composite refinements of Al-Mg-Ca-C and Al-Mg-Sr-C XRD patterns after treatment. For the AZ61 alloy, its phase composition is mainly Mg and Mg ₁₇ Al ₁₂ . After the refiner treatment, its phase composition has no obvious change, and it is still mainly composed of Mg and Mg ₁₇ Al ₁₂ . It can be seen that for the AZ61 magnesium alloy, its phase composition will not change significantly after being treated with the above three refiners.

Example 11: Grain refinement treatment of AZ91 magnesium alloy

AZ91 magnesium alloy is a cast magnesium alloy widely used in AZ series magnesium alloys. Its composition is: 8.8-9.2% Al, 0.6-0.9% Zn, 0.2-0.3% Mn, and the rest is Mg. The main characteristics of this alloy are high Al content, close to eutectic composition, good casting performance and high strength.

In this example, the three refiners Al-Mg-C, Al-Mg-Ca-C and Al-Mg-Sr-C prepared in Example 7, Example 1 and Example 4 were used to carry out the AZ91 magnesium alloy Refinement processing. The technological process before and after the melt refining treatment is the same as that of Examples 8 and 9, and the basic reaction and refining mechanism in the melt after refining treatment are basically the same as those of Example 8.

Figures 24, 25, 26 and 27 show unrefined AZ91, and AZ91 alloys treated with Al-Mg-C refiners containing only C, and Al-Mg-Ca-C and Al-Mg-Sr, respectively. -C The photo of the metallographic structure after treatment with two compound refiners. For the AZ91 magnesium alloy, the grain size is smaller due to the higher Al content. Compared with the untreated AZ91 magnesium alloy, the grain size of the AZ91 magnesium alloy treated with the refiner is only slightly refined, and the degree of refinement is about 1.2 times. It can be seen that for the AZ91 magnesium alloy, its own grain size is small, and the individual carbon inoculation refinement or alkaline earth metal and carbon composite refinement have little effect on its grain size, and the refinement effect is not significant.

Figure 28 shows the unrefined AZ91, and the AZ91 alloy was refined by the Al-Mg-C refiner containing only C, and the two composite refinements of Al-Mg-Ca-C and Al-Mg-Sr-C XRD patterns after treatment. For the AZ91 alloy, its phase composition is mainly Mg and Mg ₁₇ Al ₁₂ . After the refiner treatment, its phase composition has no obvious change, and it is still mainly composed of Mg and Mg ₁₇ Al ₁₂ . It can be seen that for the AZ91 magnesium alloy, its phase composition will not change significantly after being treated with the above three refiners.

Claims (6)

1. a composite grain finer that is used for the Mg-Al alloy is characterized in that, the percentage by weight that contains following composition is:

Al 50～60％；

C 1～5％；

Ca or Sr 5～10.5%;

Surplus is Mg.

2. the described method that is used for the composite grain finer of Mg-Al alloy of preparation claim 1 is characterized in that, specifically may further comprise the steps:

(1) melt pure Al down at 700～800 ℃, add Mg-Ca or Mg-Sr intermediate alloy by prescription, not enough Mg adds with pure Mg form, acquisition Al-Mg-Ca or Al-Mg-Sr intermediate alloy melt;

(2) Al-Mg-Ca or Al-Mg-Sr intermediate alloy melt are cooled to 600～650 ℃, in the time of stirring, slowly add graphite powder, stirred again 2～4 minutes, obtain semi-solid melt by prescription;

(3) with the semi-solid melt cast, promptly get composite grain finer of the present invention.

3. method according to claim 2 is characterized in that, the granularity of described graphite powder is at 8～15 μ m.

4. method according to claim 2 is characterized in that, the speed of the described stirring of step (2) is 200～500r/min.

5. method according to claim 2 is characterized in that, described prescription is the percentage by weight of each composition:

Al 50～60％；

C 1～5％；

Ca or Sr 5～10.5%;

Surplus is Mg.

6. method according to claim 2 is characterized in that, described graphite powder adds above stirring the whirlpool center.

Images